Controlling high brightness light emitting diodes (LEDs) with pulse width modulation (PWM) signals is a well-known and a widely implemented method of adjusting LED brightness. The concept of how a PWM signal modulates the LED brightness is straight forward. As the duty cycle of the PWM signal increases, the on-time of the LED increases and as a result more photons, per unit time, are generated. The circuitry involved typically includes a current source that delivers the desired current to the LED. The current source is then turned on and off by the PWM control signal. By doing this, the instantaneous current supplied to the LED remains constant, and it's the “time averaging” of how long the current is present versus how long the current is turned off, that determines the LED brightness.
There are numerous microprocessors available that have PWM control hardware built in, along with serial communication hardware, and a host of other useful peripherals.